Develop windows install instructions update (#1760)

* As discussed here: https://github.com/Unity-Technologies/ml-agents/issues/1706
Fixed typos on Installation-Windows.md that made instructions unclear. Added warning about overwriting drivers.

* edits

* edits, formatting

* Incorporated feedback from @vincentpierre

docs/Installation-Windows.md

 ```
 
 Lastly, you should test to see if everything installed properly and that
-TensorFlow can identify your GPU. In the same Anaconda Prompt, type in the
-following command:
+TensorFlow can identify your GPU. In the same Anaconda Prompt, open Python 
+in the Prompt by calling:
+
+```sh
+python
+```
+
+And then type the following commands:
 
 ```python
 import tensorflow as tf